So I've had a couple of people ask me about sound deadening and what they should do. Here's the basics (and I mean basic) of how it works and what you want to do for maximum noise reduction.
Basically sound deadening boils down to 3 types. Dampening, insulating and cancellation. The 3rd option is kind of out since it requires electronics, amplifiers and speakers to cancel unwanted sound. Basically it's the same noise played 180* out of phase. This is how noise canceling headphones work. The tech has been around for a while and when I was in tech school I actually built a system to do this. It worked great, it was one of my projects for the course and then a few years later companies like Mercedes, and others used this technology to quiet their vehicles.
Dampening is one of the more useful and typically you will place a material like Dynamat on large sections of panels to lower their resonant frequency below the level that causes it to easily transfer noise into the interior. Panels like the floor pans and areas like around the strut tower are areas where it helps. Doors are another area that need attention, both inner and outer panel. A lot of people will not take the time to put any material on the outer skin of the door. It's hard to get to, but the results become much better. One myth about doing this is that you cover the entire panel, you don't you cover large sections. For instance let's say the outer door skin is 36"X36" to dampen a door skin that size it's not necessary to add a 36" square piece to it add a piece roughly 18" square in the middle of the door. If there is a bar in the way then cut it in half and put one above and one below.
For the inner door usually just around the speaker is the area you are going to focus on. Then add smaller pieces to large areas on the panel, as I said before don't cover the whole thing, you are just trying to add some weight to the panel so that energy is not transferred into and through the panel easily. Now for the floorpans it's the same thing you want to add mass to the areas that are large and unsupported as they act as a sounding board and transmit sound through the panel. Again it's not necessary to cover the whole panel. The transmission tunnel is an area to add mass as well usually about 2/3's coverage. Same with under the seats and in the trunk and around the spare tire well. Usually you will already see some material in these areas in the back as well, just clean and match the size of the material over it. The trunk lid is another area to add some mass all the little cutout areas between the bracing can have pieces installed there as well. Installation is critical for it to last. Products like Dynamat are pretty stiff when cold and that's where a heat gun comes in handy,conversely you can lay the sheets in the sun and allow the sun to make the material pliable, not so easy in winter unless you have a room temperature area with a glass window like a patio door. Cleanliness is a high priority as well you need to clean the areas you are going to attach it to as well. Heating the panel helps as well and having a few tools on hand like a heat gun, a wooden roller about an inch or so wide with a handle to press the material down and some pieces of dowel rod with rounded ends to press it into corners. Use your imagination when it comes to tools.
Insulation. As you know adding insulation will help keep out noise by making it harder to get through because it is absorbed by the material. Just about any high density closed cell foam will help this. In this case you want to cover the whole panel this is where when you have gaps you have areas that are going to allow sound into the cabin. Personally when I install something like this I will use contact cement and touch up gun to spray the panel and the material wait 20 minutes and put it into place. It's hard to reposition at this point so having help to get the panel down helps. This isn't a quick afternoon kind of job this is usually accomplished in a day or two.
Another point I want to touch on is panel vibrations. As cars age the adhesives used to secure one panel to the other become brittle and break loose and allow the two panels to contact one and other. The trunk is a perfect example the bracing to outer skin will typically separate and the two panels will cause added noise. What I have always done for this is to use expanding foam and just go between the bracing and panel through the holes you have access too and spray a small amount in there in several spots this will keep the panels from making racket. You must be extremely careful though as if you add too much you will end up with the foam pushing out on the outer skin and you're pretty much screwed then. I had a guy watching as I applied this method to the trunk of a car and he decided he would just go whole Hogg and fill up the whole thing with expanding foam. Next day he comes back to our shop and has a big raised W on the trunk lid and when I asked him what he did he opened the trunk and the braces were full with about a 1/2" gap between the bracing and trunk panel. Don't be fooled by expanding foam it has a lot of power and can literally tear panels apart.
That's about all I can think of for now.
Jeff
Originally Posted by CrazyGuy03
